Capacitive switches, such as those formed by thick or thin film techniques on an insulating substrate, can be readily fabricated without moving parts to provide a reliable and economical switch. Such switches are being increasingly used on control panels for various domestic appliances such as sewing machines, microwave ovens, cooking ranges and the like and also for various industrial and commercial control systems. In many instances the capacitive switches are coupled to a large scale integrated circuit micro-processor, or to various large scale integrated circuit logic circuitry. Since large scale integrated circuits generally have only a limited number of leads which can be coupled to exterior circuitry, a problem arises when a relatively large number of switches are to be coupled to the integrated circuits. This problem can be alleviated by switch decoding systems coupled between the switches and the large scale integrated circuits that identify the actuated switches while at the same time requiring less connections to the integrated circuitry than the number of switches capable of being actuated. It is desirable that such switch decoding system be reliable and economical to fabricate. Additionally, it is desirable that such switch decoding systems be capable of distinguishing a valid actuation of a switch from spurious or unintentional switch actuations caused by noise, wiping of the switch surfaces, or the like. Further, it is also desirable that such switch decoding systems enable the simultaneous actuation of two or more switches to be readily detected.
Accordingly, an object of this invention is to provide an improved capacitive switch system.
Another object of this invention is to provide an improved capacitive switch system that can be economically fabricated from integrated circuits.
A further object of this invention is to provide an improved capacitive switch system that permits the number of switches utilized to be greater than the number of output leads needed to identify switch actuations.
A still further object of this invention is to provide an improved capacitive switch system that enables an actual switch actuation to be readily distinguished from spurious switch actuations.
Still another object of this invention is to provide an improved capacitive switch system that enables the simultaneous actuation of two or more switches to be readily detected.